1. Field of the Invention
The invention relates to quantum well structures for semiconducting devices, the structures including a strain-layer superlattice, and to devices employing the superlattice for various applications including for metal oxide-semiconductor field effect transistors.
2. Description of the Related Art
Prior publications concerning superlattices and quantum well structures are listed as follows, and the disclosure of each of said prior publications is incorporated herein by reference:
1. L. Esaki and R. Tsu, IBM J. Res. and Dev. 14, 61 (1970). PA0 2. R. Tsu and L. Esaki, Appl. Phys. Lett. 22, 562(1973); L.L. Chang, L. Esaki and R. Tsu, ibid 24 593(1974). PA0 4. J.W. Matthews and A.E. Blakeslee, J. Crystal. Growth 32 265(1976). PA0 5. G.C. Osbourn, J. Appl. Phys. 53, 1586(1982). PA0 6. E.H. Poindexter & P.J. Caplan, in "Ins. Films on Semi." (Springer, Berlin 1981) p. 150. PA0 7. E.H Nicollian and R. Tsu, U.S. Pat. No. 5,051,786, Sep. 24, 1991; R. Tsu, E.H. Nicollian, and A. Reisman, Appl. Phys. Lett. 55, 1897(1989). PA0 8. Q.Y.Ye, R. Tsu and E.H. Nicollian, Phys. Rev. B44, 1806(1991). PA0 9. R. People, IEEE Q.E. 22, 1696(1986). PA0 10. D.G. Deepe et al., Appl. Phys. Lett. 51, 637(1987).
3. J.P. van der Ziel et al., IEEE Q.E. 22 1587(1986).
For a general review of quantum devices, see F. Capasso et al. IEEE, Transactions on Electron Devices 36, 2065(1989) and F. Sols et al., Appl. Phys. Lett. 54 350(1989), the disclosure of each being incorporated herein by reference.
Electronic industries have entered into a new domain of small devices dictated by quantum mechanical effects. Whenever the electron mean free path exceeds the physical dimensions, the wave nature of the electrons play a dominant role in the operations of these devices such as the now-famous superlattice (see publication 1 above) and quantum well structures (see 2 above). All these new devices involve electrons confined in a quantum well between two energy barriers. To date, the wells and barriers in general, utilize a lattice matched system such as the GaAs/GaAlAs superlattices, or a strain-layer system such as AlGaSb/GaSb heterojunction lasers (see 3 above). As long as the thickness of the strain-layer system is kept below certain values determined by the stored strain energy in those layers, a defect-free superlattice is possible for lattice mismatched systems (see 4 and 5 above). Since the backbone of the electronic industry is in silicon technology, the involvement of silicon is required in order for quantum devices to play an important role. It is well known that the importance of the metal oxide-semiconductor field effect transistor (MOSFET)owes its success to the low interface defect density of the a-SiO.sub.2 (amorphous SiO.sub.2) and Si interface (see 6 above). The problem is that once an amorphous layer is grown, it is impossible to grow subsequent silicon epitaxially.
Therefore it is not possible to realize quantum devices with the Si/a-SiO.sub.2 system, except where microcrystalline Si is involved (see 7 and 8 above). This invention involves the creation of alternate layers of SiO.sub.2 and Si, as a strain-layer superlattice, serving as energy barriers for confinement. This is possible provided the layer thickness is no more than a couple of mono-atomic layers. Specifically, we propose a structure consisting of a quantum well formed by silicon with energy barriers formed by monolayers of SiO.sub.2 /Si strain-layer superlattice. This new scheme opens the door for a silicon based family of new quantum devices.
A superlattice consisting of Si and SiO.sub.2 should be the ideal choice; however as SiO.sub.2 grows thicker, strain due to the extremely high lattice mismatch dominates and resulting SiO.sub.2 becomes amorphous, preventing the subsequent growth of epitaxial layers. Matthews and Blakeslee (4 above) showed that if the thickness of the strain layer is thin enough the stored energy, if released, is below the creation energy for defects such as dislocations, the strain layer is then PERFECT, and subsequent growth of the epitaxial layer can proceed. This idea is responsible for many injection lasers (see 10 above).